MEMS integrated pressure sensor and microphone devices and methods of forming same

Abstract

A method embodiment for forming a micro-electromechanical (MEMS) device includes providing a MEMS wafer, wherein a portion of the MEMS wafer is patterned to provide a first membrane for a microphone device and a second membrane for a pressure sensor device. A carrier wafer is bonded to the MEMS wafer, and the carrier wafer is etched to expose the first membrane for the microphone device to an ambient environment. A MEMS substrate is patterned and portions of a first sacrificial layer are removed of the MEMS wafer to form a MEMS structure. A cap wafer is bonded to a side of the MEMS wafer opposing the carrier wafer to form a first sealed cavity including the MEMS structure. A second sealed cavity and a cavity exposed to an ambient environment on opposing sides of the second membrane for the pressure sensor device are formed.

What is claimed is: 
     
       1. A method for forming a micro-electromechanical (MEMS) device comprising:
 providing a MEMS wafer, wherein a portion of the MEMS wafer is patterned to provide a first membrane for a microphone device and a second membrane for a pressure sensor device; 
 bonding a carrier wafer to the MEMS wafer; 
 etching the carrier wafer and the MEMS wafer to expose both surfaces of the first membrane for the microphone device to an ambient environment; 
 patterning a MEMS substrate and removing portions of a first sacrificial layer of the MEMS wafer to form a MEMS structure; 
 bonding a cap wafer to a side of the MEMS wafer opposing the carrier wafer to form a first sealed cavity including the MEMS structure; and 
 forming a second sealed cavity and a cavity exposed to an ambient environment on opposing sides of the second membrane for the pressure sensor device. 
 
     
     
       2. The method of  claim 1 , a pressure level of the first sealed cavity is defined by a bonding process between the cap wafer and the MEMS wafer. 
     
     
       3. The method of  claim 1 , wherein forming the second sealed cavity and the cavity exposed to an ambient environment on opposing sides of the second membrane for the pressure sensor device comprises the bonding the carrier wafer to the MEMS wafer and etching the cap wafer. 
     
     
       4. The method of  claim 3 , wherein forming the second sealed cavity and the cavity exposed to an ambient environment on opposing sides of the second membrane for the pressure sensor device further comprises removing a temporary handle wafer from the cap wafer. 
     
     
       5. The method of  claim 1 , wherein forming the second sealed cavity and the cavity exposed to an ambient environment on opposing sides of the second membrane for the pressure sensor device comprises bonding the cap wafer to the MEMS wafer and etching the carrier wafer. 
     
     
       6. The method of  claim 1 , further comprising providing the cap wafer, wherein providing the cap wafer comprises:
 providing a semiconductor wafer having a metal line; 
 forming a conforming oxide layer over the metal line; 
 forming a film layer over the conforming oxide layer; and 
 forming a first plurality of bonds over the film layer. 
 
     
     
       7. The method of  claim 6 , further comprising forming contact plugs electrically connecting at least a portion the first plurality of bonds to the metal line. 
     
     
       8. The method of  claim 6 , further comprising shallow etching a portion of the film layer to form one or more bumps, and wherein bonding the cap wafer to the MEMS wafer comprises aligning the one or more bumps to the MEMS structure. 
     
     
       9. The method of  claim 6 , wherein bonding the cap wafer to the side of the MEMS wafer opposing the carrier wafer comprises a eutectic bonding process between the first plurality of bonds and a second plurality of bonds disposed on the side of the MEMS wafer opposing the carrier wafer. 
     
     
       10. The method of  claim 1 , further comprising forming voids in the first sacrificial layer. 
     
     
       11. The method of  claim 1 , wherein removing portions of the first sacrificial layer comprises a vapor hydrogen-flouride (vapor HF) etching process. 
     
     
       12. The method of  claim 1 , wherein the cap wafer is a CMOS wafer comprising active circuits. 
     
     
       13. The method of  claim 1 , wherein bonding the carrier wafer to MEMS wafer comprises using a bonding layer of the MEMS wafer as an interface, and wherein providing the MEMS wafer further comprises:
 forming the first sacrificial layer over the MEMS substrate; 
 forming a polysilicon layer over the first sacrificial layer; 
 patterning the polysilicon layer to form the first and second membranes; 
 forming an etch stop layer over the polysilicon layer; 
 forming a second sacrificial layer over the etch stop layer; and 
 forming the bonding layer over the second sacrificial layer. 
 
     
     
       14. The method of  claim 1 , wherein bonding the carrier wafer to the MEMS wafer comprises a fusion bonding process. 
     
     
       15. A method for forming a micro-electromechanical (MEMS) device comprising:
 providing a MEMS wafer, wherein a portion of the MEMS wafer is patterned to provide a first membrane for a pressure sensor device; 
 bonding a carrier wafer to the MEMS wafer; 
 forming a first sealed cavity on a first surface of the first membrane for the pressure sensor device; 
 forming first and second MEMS structures by patterning a MEMS substrate of the MEMS wafer, wherein the first MEMS structure is disposed over the first membrane; 
 forming a polysilicon layer over a surface of the MEMS wafer opposing the carrier wafer, wherein a portion of the polysilicon layer is disposed over the first MEMS structure and is patterned to provide a second membrane for a microphone device; 
 bonding a cap wafer to the polysilicon layer to form a second sealed cavity including the second MEMS structure; and 
 exposing the second membrane for the microphone device and a second surface of the first membrane for the pressure sensor device to an ambient environment. 
 
     
     
       16. The method of  claim 15 , further comprising forming a third MEMS structure by patterning the MEMS substrate, and wherein the bonding the cap wafer to the polysilicon layer defines a third sealed cavity including the third MEMS structure. 
     
     
       17. The method of  claim 15 , wherein bonding the carrier wafer to the MEMS wafer forms the first sealed cavity. 
     
     
       18. The method of  claim 15 , wherein exposing the second membrane for the microphone device and the second surface of the first membrane for the pressure sensor device to an ambient environment comprises etching the cap wafer and removing a temporary handle wafer from the cap wafer. 
     
     
       19. The method of  claim 15 , wherein bonding the carrier wafer comprises a fusion bonding process, and wherein bonding the cap wafer comprises a eutectic bonding process. 
     
     
       20. A method for forming a micro-electromechanical (MEMS) device comprising:
 providing a MEMS wafer, wherein a portion of the MEMS wafer is patterned to provide a first membrane for a first MEMS device and a second membrane for a second MEMS device; 
 bonding a carrier wafer to a first side of the MEMS wafer to form a second sealed cavity, wherein a first surface of the second membrane is exposed to a sealed pressure level of the second sealed cavity; 
 bonding a cap wafer to a second side of the MEMS wafer opposite the first side to form a first sealed cavity; 
 exposing both surfaces of the first membrane to an ambient environment; 
 and 
 exposing a second surface of the second membrane to the ambient environment.